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Mon, 22 Dec 2025 09:02:19 -0500 (EST) Date: Mon, 22 Dec 2025 14:02:18 +0000 From: Kiryl Shutsemau To: Muchun Song Cc: Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Andrew Morton , David Hildenbrand , Matthew Wilcox , Usama Arif , Frank van der Linden Subject: Re: [PATCHv2 02/14] mm/sparse: Check memmap alignment Message-ID: <4ctnfkw5zqneume6px2wqgdgusfdricr4uuonv7bfjheknrt2g@fdb5ceiiar4q> References: <20251218150949.721480-1-kas@kernel.org> <20251218150949.721480-3-kas@kernel.org> <430d554c-840f-4813-b715-5191d74571a0@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <430d554c-840f-4813-b715-5191d74571a0@linux.dev> X-Stat-Signature: fbxqx3njge1y3qf7jnkzp6qziuu68h3g X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D842D40027 X-HE-Tag: 1766412142-245610 X-HE-Meta: U2FsdGVkX19lraJa2rBbsi5FKJZy+u/XKftDsUoT5ITQnsMiaur45vtSZT2Uveuxu89sC8MGpDh0zI9BMeZr/03oVMZAuamcpcfjRO9jJG5uTTqy/6u2NjyPVoY5e7IJFkC1HOtwBExVwJcN9GPkhlIJPDOWwMOOhWsmSyrF5kN0hTImTe9BsBp6W6W11QJTwy4iFyypMAAdHHuyNtMdh3ap6wask6c0dOn0IZL2US0r7XkEaTCKlXudQpNctxacE+lYh6WPB5K1ZeUrOaduyftGEzW8v0xf9Xdyksz2lB6G8awKB2SEomkpYrpJ75SiwjJ8/zbhlazMeENpRDXDzUKMQsqhtZUtKBh4V1Ynl7OoL5oc/indbNE98gLmeLbkXNcrA/Nz0oiTpRorjS+Vl9c48ID6gY4bh6oe4TT5inMYJ8dNcptutjJ3FE3tEKH7HSsYDX5KgiMggdz7na9xv0LTh/NYN90hy3f1Tqhaz2khHEK1FrrPoGF64DnuTp9fBY25CduIKQsCFPWHMEWjbf8RVKDwu5AsYHBk6mykTNpOKFw0ngz6YSWnxLIZJmCQroYnI5MckY5DR5xbLyBwq4DSESF0Rqcd2od4TG7CUBXiIsCrUjxKTTJMinKFUHDRA/3sCSNR4qPSPW0uqBLmYhlaS63vYTzx7hliDX4wxnQXc0MVAnq1EryPTlvlW7DPcCnoKx/UrA47YAiznZvMfLlqq0PbvfGfmUhvFV4oSeKRWSWFywovkgJSAHzdQjBg1KmV35c19Fh8X1iO1GkJK/x0wJewhjW8I0FrkOWhdlWwVDEwOJOBBhHnpvcDpKMSAHxkKuT8t1vzarHMNkHba1wJy8ntajPFPACbvMrr2zGUF4FZbSZJYhwtfsCeh8Mw7JrFIzwbFL0/or/nwbc8v2HySFpck96JNJzUyxI4uF7plp3mmGLsljV15WPfVEYw1krND5IH6Fb/T4vc5ps E0WsX/SD eX0Kvp8cZj/setckaQymdtcgh8LRVtD7be07oPzEBHymPxe1tTP8DZNvAuVS4ewS9s9z9I3dlULeRj4oNBRQKnaKUMz/joZEzSs5AvxOvAxXzW0A5DFyOgaxILpNH/Zt6vS+WEhJGgeV1oitpxbl27e4uHpIsg0YFULufVFQi0x3/DJWCbYePI2qR30+B+MJayPxdKGtiy29SoenEjhWwQILTr2DcKoBbZ+tpEVIphMvhoptObSS7ViYo2WR4BfgCKAcvW7PQyCuCDk4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Dec 22, 2025 at 04:34:40PM +0800, Muchun Song wrote: > > > On 2025/12/18 23:09, Kiryl Shutsemau wrote: > > The upcoming changes in compound_head() require memmap to be naturally > > aligned to the maximum folio size. > > > > Add a warning if it is not. > > > > A warning is sufficient as MAX_FOLIO_ORDER is very rarely used, so the > > kernel is still likely to be functional if this strict check fails. > > Different architectures default to 2 MB alignment (mainly to > enable huge mappings), which only accommodates folios up to > 128 MB. Yet 1 GB huge pages are still fairly common, so > validating 16 GB (MAX_FOLIO_SIZE) alignment seems likely to > miss the most frequent case. I don't follow. 16 GB check is more strict that anything smaller. How can it miss the most frequent case? > I’m concerned that this might plant a hidden time bomb: it > could detonate at any moment in later code, silently triggering > memory corruption or similar failures. Therefore, I don’t > think a WARNING is a good choice. We can upgrade it BUG_ON(), but I want to understand your logic here first. -- Kiryl Shutsemau / Kirill A. Shutemov